Trunking system.



HENRY 1. CLAUSEN, F MOUNT VERNON, NEW YORK, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

Specification of Letters Patent.

. TRUNKING SYSTEM.

Patented July 9, 1918.

To all whom it may concern: I

Be it known that I, HENRY P. CLAUSEN,

' a. citizen of the United States, residing at Mount Vernon, in the county of Westchester and State of New York, have invented certain new and useful Improvements in Trunking Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to trunking systems, and is particularly adapted to automatic telephone exchanges.

Experience has shown that in a given installation a certain number of trunk outlets for originating calls are required for a group of subscribers lines, the number of outlets being some percentage less than 100 of the lines they serve. The percentage required is larger, the smaller the group of lines, and it is therefore desired, where economy in outlets is important, to arrange the subscribers lines in as large groups as practical.

This invention provides an organization of lines, trunks and switches in main and subgroups with overflow trunks between the subgroups of each main group, together with a secondary group of switches with trunks between the rimary switches and the secondary switc es, and with overflow trunks between the subgroups of secondary switches.

This organization reduces the ultimate trunks or connecting circuits to which the calls from the subscribers lines are dis-' tributed, to the percentage that would be required for a single large group of sub.

scribers lines having primary switches only of large capacity leading directly to the ultimate trunks or connecting circuits.

The invention will be more readily understood by reference to the accompanying drawing, wherein a trunking system is illustrated in a diagrammatic manner without showing any details of circuits and apparatus for the various switching functions. It will be understood that any of the numerous well-known types of switching apparatus may be used for the purpose.

In the drawing A, B, C and D represent main groups of subscribers lines and primary switches, and each of these main groups, say A, is divided into two subgroups, a and a Each subgroup comprises a number of subscribers llnes and switching apparatus whereby any calling line, say line 1 of subgroup a by its terminal 2 may betrunks, such as the trunk 3 leading directly to the group F of secondary switches, or if all such trunks are in use, with any one of a plurality of overflow trunks, such as the trunks 4 and 5, leading to terminals 7 and 8 respectively of the other subgroup a? of the main group A. This other subgroup a is a duplicate of the first subgroup a and it is provided likewise with trunks, such as the trunk 11, leading directly to the secondary group of switches F and a number of overflow trunks, such as the trunks 12 and 13, leading to the first subgroup a.

F and G represent maingroups of secondary switches, and each of these groups, say F, is divided into two subgroups, f and f. The trunks, of which 3 and 11 are typical, may be extended, as shown, from the main group A of primary switches to one of the subgroups f of the main group F of secondary switches. This main group F of secondary switches is like in arrangement but larger in capacity than each main group of primary switches. It'serves to extend the calls received over the trunks from two of the main groups A and B of primary switches togother trunks, such as the trunks 15, 16. The group of trunks represented by trunk 15 is somewhat larger thin, but not twice as large as the group of trunks represented by the trunk 3, and likewise the group represented by trunk 16 is somewhat larger than, but not twice as large as the group represented by the trunk 11. Overflow trunks, such as the trunks 17 18 and 19, are provided between the subgroup f of the main group F of secondary switches and the subgroup f thereof, and other overflow.

trunks 22, 23 and 24 extend between the subgroup f and the subgroup 7.

The trunking system as .above outlined may be extended to any desired extent. For example, main groups A, B, C and D of primary switches may be divided into two grand groups, A, B being one grand group and C, D another. Group G of secondary switches serves to extend calls from the grand group C, Din the same way that group F of secondary switches extends calls from grand group A, B.

Finally a group of tertiary switches H may be provided for receiving calls extended by the secondary groups F and G to the trunks 15, 16, etc.., and distribute these calls to a single group of ultimate trunks, of

which trunk 26 is typical, common to the use of all the subscribers lines of primary groups A, B, C and D.

Each subscribers line of any primary subgroup, by -means of the trunking'an'angement of this invention, has access to any one of these ultimate trunks. The call may be extended by anyone of the eight subgroups of primary switches either directly to a secondary switch 'or indirectly thereto through one of the overflow trunks, such as 4 or 5, and by a secondary switch either directly to a tertiary switch or indirectly thereto through one of the overflow trunks such as, 17, 18 or 19, and finally from and by means of a tertiary switch to any one of the common trunks, such as 26.

Let it be assumed that the total number of final outlets, such' as the trunk 26 required to take care of the maximum trafiic froma large group of subscribers lines, is 100.

It may be ascertained mathematically just how many trunks would be required in the group represented by trunks 15 and 16 to take care of the maximum traflic of the subscribers lines entering primary groups A and B. This number is approximately 56. There would thus'be 112 trunks incoming to the tertiary switches H and 100 outgoing. It may also be ascertained what is the number of trunks required in the group represented bythe trunks 3 and 11 to take care of the maximum trafiic of calls from the lines entering a single main primary group such as A. This number is approximately 34. It will thus be seen that there are 136 trunks extending between the primary switches and the secondary switches. It can also be ascertained what isthe number of trunks required for taking care of the calls received from the subscriberslines included in each subgroup, say a and this number is approximately 20.

This system of trunking, in the example given, reduces materially the number of ultimate trunks required over a system wherein a large number of separate small groups are provided. By providing subgroups of primary switches and subgroups of secondary switches with overflow trunks between the subgroups and a group of tertiary switches the ultimate number of trunks a or connecting circuits is reduced from 160 These figures are approximately correct for one set of conditions. The traffic problem may be-worked out mathematically for any similar conditions met with in practice and the invention may be applied with similar results.

What is claimed is:

1. In a trunking system, a plurality of main groups of primary switches arranged in subgroups, a main group of secondary switches arranged in subgroups, each sub group of secondary switches being normallyindividual to a different one of said main groups of primary switches, first choice trunks for-the switches of each of the subgroups of each main group of primary switches leading to the switches of group of secondary switches leading to the switches of another subgroup of said main group of secondary switches.

2. In a trunking system, a plurality of main groups of prlmary switches arranged.

in subgroups, a main group-of secondary switches arranged in subgroups, each subgroup of secondary switches being normally individual to a difierent one of said main groups of primary switches, first choice trunks for all the switches of each sub roup of each main group of primary switches leading to switches of the subgroup of secondary switches normally individual to such main group, second choice trunks for all the switches of each subgroup of each main group of primary switches leading to a portion of the switches of another subgroup of the samemain group of primary switches, first choice trunks for all the switches of each subgroup of said main group of secondary switches outgoing from said main group, and second choice trunks for all the switches of each subgroup of the main group of secondary switches leading in subgroups, a main' group of secondany switches arranged in subgroups, each of said secondary sub oups being normally individual to a di erent main roup of primary switches, first choice trunlis for all the switches of each subgroup of each main group of primary switches leading to switches of the sub roup of secondary switches normally in ividual to such primary main group, second choice trunks for all the switches of each subgroup of each main group of primary switches overflowing to a portion of the switches of another subgroup of the same main group of primary switches, subscribers lines terminating directly in the remaining switches of -each primary subgroup, first choice trunks the subgroup of secondary switches norfor all the switches of each subgroup of said main group of secondary switches outgoing therefrom, and second choice trunks for all switches of each subgroup of secondary switches overflowing to switches of another subgroup of said secondary main group.

4. In a trunking system, main groups of primary switches arranged in subgroups, main groups of secondary switches arranged in subgroups, each of said secondary subgroups being normally individual to a difi'erent main group of primary switches, a group of tertiar switches, first choice trunks for all switc es of each subgroup of each main group of primary switches leading to switches of the subgroup of secondary switches normally individual to such primary main group, second choice trunks for all switches of each subgroup of primary switches leading to switches of another subgroup of the same main primary group, first choice trunks for all switches of each subgroup of each main group of secondary switches leading to said tertiary group, and second choice trunks for all switches of each subgroup of each main group of secondary switches leading to switches of another subgroup of the same main group of secondary switches.

In witness whereof, I hereunto subscribe my name this 2d day of March A. D., 1915.

' HENRY P. CLAUSEN.

Witnesses:

E.EDLER, K. L. STAHL. 

